Lichen

Lichen is a composite organism that arises from algae or cyanobacteria (or both) living among filaments of a fungus in a symbiotic relationship. The combined life form has properties that are very different from the properties of its component organisms. Lichens come in many colors, sizes, and forms. The properties are sometimes plant-like, but lichens are not plants. Lichens may have tiny, leafless branches (fruticose), flat leaf-like structures (foliose), flakes that lie on the surface like peeling paint (crustose), or other growth forms.

Classification

Lichen classification is complex and still subject to debate. It is generally agreed that lichens are classified as fungi, under the genus and species of the host fungus. The algal or cyanobacterial component of a lichen also has its own genus and species.

Morphology

Lichens may appear as a thin, crust-like covering on rocks, soil, tree bark, or leaves. They may also appear as shrubby or leafy growths, or hanging strands. The body of a lichen, known as a thallus, is generally composed of a fungal filament (hyphae) network, within which are embedded the algal or cyanobacterial cells.

Reproduction

Lichens reproduce either by tiny pieces of the lichen breaking off and growing somewhere else (vegetative reproduction) or by the production of fungal spores. The fungal partner is solely responsible for sexual reproduction.

Ecology

Lichens play an important role in the environment. They are pioneers on bare rock, and they help to turn rock into soil. Lichens also provide food and shelter for a variety of organisms.

Uses

Lichens have many uses. They have been used in making dyes, perfumes, and medicines. Some lichens are also used as indicators of air pollution.

See also

• Mycorrhiza
• Endosymbiont
• Symbiosis

References

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